1. Field of the Invention
The invention relates to a sensor device for establishing the relative position of two mutually displaceable objects, a method of automatically determining a position of a displaceable robot with respect to an object with the aid of the sensor device, and a use of the sensor device and an application of the method for controlling a mounting robot for a line of machines and/or devices, in particular for the automatic processing or treatment of electronic chips.
2. Discussion of the Prior Art
FIG. 1 schematically shows in perspective a line of machines for the automatic processing and/or of devices for the automatic treatment of electronic chips according to the prior art.
FIG. 2 shows in a schematic side view selected elements of the installation shown in FIG. 1 according to the prior art.
The journal "productronic 1/2-1991", page 112 and "European Semiconductor", October 1990, disclose the line of machines schematically represented in perspective in FIG. 1 for the automatic processing and of devices for the automatic treatment of electronic chips. The machines B1-B4 are, for example, "die bonders" and "wire bonders" for establishing electrical connections on the chips, and the devices E1-E2 are, for example, continuous furnaces for the curing of plastics and devices for the intermediate storage of the chips. The chips to be processed or to be treated are contained in magazines M when they are transported, fed to the machines B1-B4 or devices E1-E2 and prepared therein for processing or treatment and also for transporting away after the processing or treatment.
The machines B1-B4 and devices E1-E2 are set up in series. Arranged behind this series, with regard to the transport of the magazines, is a rail device T, on which there runs a mounting robot R, which grips, moves, positions and releases the magazines M as required.
In FIG. 2, the machine B1, the rail device T and the mounting robot R are represented in a schematic side view. The mounting robot R travels rectilinearly and horizontally on the rail device T. A gripper G for the magazine M is supported movably on the mounting robot R by means of an advancing carriage V and a lifting carriage H. The advancing carriage V is movable on the mounting robot R horizontally and orthogonally to the rail device T towards the machine BI and away from it. The lifting carriage H is movable vertically on the advancing carriage V. Consequently, the gripper G can be moved with three Cartesian degrees of freedom or directions of movement with respect to the machine B1 in order to bring the magazine M to the intended magazine position P1 or P2 at the machine B1 and unload it there, or to grip it there and lead it away from there.
This entails the problem of automating the movements of the mounting robot R.
The machines B1-B4 are namely set up, changed and adjusted in accordance with the requirements of fabrication. The individual machines are then admittedly aligned as well as possible at right angles to the rail device T or to the running direction of the mounting robot R, but are not mechanically connected directly and in a predetermined way to the rail device T. The only common reference is the floor plane; moreover, the machines M or their magazine positions P1-P2 may be arranged at various non-standardized heights above the floor and at various non-standardized distances from the rail device T. Under these circumstances, to automate the movements of the mounting robot R it is necessary to make the mounting robot R itself learn the magazine position P1-P2 and determine the corresponding set position of the gripper G, otherwise the magazine positions P1-P2 would have to be measured after each change and entered into the control of the mounting robot R as a corresponding default value, which would be extremely complex. To detect the magazine positions concerned, sensor devices are necessary.
A sensor device which can be used for this is disclosed, for example, by the brochure "LN110/120" of the Namco company. It essentially comprises a laser as light source, a constantly rotating mirror, a photodetector and an angle-reference detector, which are all integrated in a measuring device, and also a retro-reflector and, if appropriate, code plates, which are attached on an object, and a microprocessor, one of the functions of which is that of a computing circuit. Using the constantly rotating mirror, the laser beam periodically scans a predetermined angle of view. The retro-reflector returns the laser beam to the photodetector. As long as the laser beam scanning at a constant rate meets the retro-reflector, the photodetector generates a retro-reflection pulse, the duration of which is inversely proportional to the distance of the retro-reflector from the photo-detector. The closer the retro-reflector is to the photodetector, the greater the pulse duty factor of retro-reflection duration to dark interval in a period of the scanning. On the other hand, the angle-reference detector generates an angle-reference pulse with each period of the scanning. If, during the course of scanning, the laser beam reaches the retro-reflector, a retro-reflection pulse begins. The time between the beginning of the angle-reference pulse and the beginning of the retro-reflection pulse is directly proportional to the angular position of the retro-reflector with respect to the direction of the laser beam at the beginning of the angle-reference pulse. Consequently, the angular position or the distance of the retro-reflector can be measured contactlessly, provided that the dimension of the retro-reflector in the plane of the scanning to the laser beam or orthogonally to the axis of the rotating mirror is known. If the known retro-reflector is, furthermore, arranged at a defined point of an object, or if a known object is arranged between the known retro-reflector and the photodetector in such a way that it interrupts the laser beam, the computing circuit can calculate the distance and position of the object on the same principle. In this case, there may be arranged on the object additional code plates, by which the computing circuit can identify the object.
In the immediately following text, to simplify explanations it is assumed that an object or a code plate always lies in a plane oriented essentially orthogonally to the angle bisector of the angle of view. If the object or code plate is oriented askew by a known angle to the angle bisector of the angle of view, the distances calculated by the computing circuit from the object or code plate to the optical center of the sensor device are to be corrected by the sine of this angle.
If, in a line of machines for the automatic processing and of devices for the automatic treatment of electronic chips, the mounting robot R is provided with a sensor device of the type specified above, the computing circuit supplies the information specifying the distance and position of the machines B1-B4 and devices E1-E2, but only in the plane of the scanning with the laser beam or orthogonally to the axis of the rotating mirror. To automate the movements of the mounting robot R there is still missing the information in the direction parallel to the axis of the rotating mirror or orthogonally to the plane of the scanning with the laser beam, since the information obtained with a sensor device of the type specified above is only two-dimensional, which is inadequate for automating the movements of the mounting robot R.
To overcome this inadequacy by combining two sensor devices of the type specified above is complex and, furthermore, disruptive owing to the restricted space around the mounting robot.